Projection Apparatus and Method for Pepper&#39;s Ghost Illusion

ABSTRACT

An image projection apparatus includes a projector, a frame, and a partially transparent screen. The frame retains the screen under tension, such that the screen is inclined at an angle with respect to a plane of emission of light from the projector. The screen has a front surface arranged such that light emitted from the projector is reflected therefrom. The projector projects an image such that light forming the image impinges upon the screen such that a virtual image is created from light reflected from the screen, the virtual image appearing to be located behind the screen.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 13/011,452 filed on Jan. 21, 2011 (now allowed), which is acontinuation of U.S. application Ser. No. 10/599,553, filed on Sep. 30,2006 (now U.S. Pat. No. 7,883,212), which is a U.S. National Phase entryof PCT/GB2004/001414, filed on Apr. 1, 2004, the disclosures of whichare incorporated herein by reference in their entirety.

This invention relates to a projection apparatus and method. Moreparticularly, but not exclusively, it relates to a projection apparatusarranged to project an image of an object upon an inclined, partiallyreflective, screen so as to give a false perception of depth and amethod for constructing such an apparatus.

BACKGROUND OF THE INVENTION

The projection of an image upon a partially reflective screen such thatis observable by a viewer positioned in front of the screen is known,the so-called “Peppers ghost” arrangement that is known form fairgroundshows.

This has been applied to publicity and promotional displays where apresenter resides behind an inclined, partially reflective screen,typically a tensioned foil, onto which an image of, for example, a motorvehicle is projected, via at least one reflective surface, see forexample EP 0799436. The location of the presenter behind the projectedimage has a number of inherent advantages over systems where thepresenter stands in front of a screen, not least of which is that thepresenter does not obscure the projected image when walking across theprojected image. Additionally, the use of an inclined screen results ina viewer of the image perceiving the image as having depth rather thanmerely being a two dimensional image, for example where a motor vehicleis seen to rotate upon a turntable.

However, current image projection apparatus' do have a number ofproblems associated with them, for example, mounting of the foil canprove difficult which in turn leads to uneven tensioning of the foil andwrinkles upon the foil, that impair the viewed quality of the imageprojected onto the foil. Also, in mounting the foil the foil must belaid out upon a clean dust free piece of cloth or plastic sheet, whichis larger than the foil, in order to prevent particles adhering to thefoil, such particles can scratch the surface of the foil and impair theviewed quality of the projected image or act as scattering centres fromwhich projected light is incoherently scattered, thereby detracting fromthe viewed quality of the image as this scattered light does notcontribute to the viewed image.

Also, as the illusion of peppers ghost relies on the reflected imageformed by light contrasting with its immediate surroundings andbackground. The stronger the reflected image, the more solid thatreflected image looks, the more vibrant the colours will be, and themore visible the reflected image is to an audience. In circumstanceswhere the presenter may be unable to control high levels of ambientlight forward of the foil, e.g. from an auditorium at a trade show, thehigh level of ambient light results in significant levels of reflectionof the ambient light from the screen detracting from the strength of thereflected image over the background. In these circumstances a brightprojector (8000 lumens+) is desirable. However, the use of a brightprojector results in unwanted light hitting the projection surface andreflecting through the foil to create a milky hue upon the stage andaround the area where the reflected image appears.

Another problem with current image projection apparatus is thatprojectors used with such apparatus are very powerful, typically 8,000to 27,000 lumens and consequently project a significant amount of lightinto areas of an image where there is no object within the image. Thisis an inherent feature of projectors and results in low contrast ratioswhich leads to a milky hue spread over the part of the film where theprojector is creating an image when the projector is switched on. Themilky hue is clearly undesirable as it detracts from the viewer'sperception that there is no screen present.

The level of the milky hue relative to the brightness of the image is,at least partially, determined by the level of contrast ratio offered inthe projector. The higher the contrast ratio, then the brighter theimage can be relative to the brightness level of the milky hue. Evenprojectors with contrast rations as high as 3000:1 still emit a milkylight hue when used in a “Pepper's Ghost” arrangement.

A further problem associated with some projectors is the “keystone”effect, in which distorted, typically elongated, images (up and down)occur due to angled projection. This is of particular relevance wheredepth perception is of importance. The solution employed in modern,expensive projectors is to employ digital correction of keystonedistortions. However, older, less-expensive or even some specialist HighDefinition projectors do not employ such digital keystone correction andare therefore difficult to configure for use with current imageprojection apparatus. High definition (HD) projectors do not offerkeystone adjustment because when keystone correction is attempted inconjunction with the increased number of pixels about an image's edgecauses the pixels about the edge of the image to appear ‘crunched’.Additionally, when processing moving images HD projectors compromiseprojector processing speed. When the processing power is used to carryout both keystone correction and motion processing the image is seen tojerk during movements, an effect known as “chokking”. In general, it canbe said that the use of electronic keystone correction to alter a videoimage will result in the degradation of picture quality compared to animage which is not subject to such a process.

Additionally, current systems do not allow for the projected image toapparently disappear and re-appear from behind a solid 3D object placedupon the stage, as the screen lies in front of the presenter and closestto the viewing audience.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided aimage projection apparatus comprising a projector, a frame, and an atleast partially transparent screen:

the frame being arranged to retain the screen under tension, such thatthe screen is inclined at an angle with respect to a plane of emissionof light from the projector;

the screen having a front surface arranged such that light emitted fromthe projector is reflected therefrom; and

the projector being arranged to project an image such that light formingthe image impinges upon the screen such that a virtual image is createdfrom light reflected from the screen, the virtual image appearing to belocated behind the screen.

Such an apparatus is advantageous over present systems in that thescreen need not be coated with an expensive, partially reflectivecoating, an angular dependence of reflectivity of transparent dielectricmaterials can be used to bring about partial reflectance of theprojected image. Thus, this apparatus simplifies the manufacture of suchsystems and also reduces their production costs. Additionally, the useof a frame frees the screen from having to be fixed directly to aceiling, or a floor, and therefore increases the utility of apparatusover the prior art systems.

The screen may be a foil. The foil may be rolled about a cylinder whennot in use. The screen may be inclined at approximately 45° to the planeof emission of light from the projector. The screen may comprise apartially reflective layer upon the front surface.

The use of a foil screen reduces the weight of the apparatus, thisallows ready transportation of the apparatus between sites. Rolling thefoil onto a cylinder when not in use serves to protect the foil fromdamage during transportation and also allows ready transportation of theapparatus between sites. The use of a partially reflective screen canincrease the degree of light reflected from the screen and can increasethe audience perceived strength of the virtual image.

The screen may be attached to the frame at the screen's upper and/orlower edges. The frame may comprise first and second retention membersarranged to sandwich an edge region of the screen therebetween. At leastone of the first and second retention members may comprise an abrasivecoating, typically sandpaper, arranged to contact the screen. The firstand second retention members may comprise respective openingstherethrough that may be arranged to collocate with openings inrespective jaws of clamping members attached to tensioning straps, theopenings may be arranged to receive a fixing means so as to clamp thescreen between the first and second retention members. The tensioningstraps may be attached to a truss arrangement and may be adjustable suchthat the tension of the screen within the truss arrangement can bevaried about the periphery of the screen. Preferably, the retentionmembers are substantially parallel to truss members comprising the trussarrangement.

The use of a variable tensioning arrangement allows wrinkles upon thescreen to be minimised, and ideally eradicated to present a smoothsurface for upon which the image can be projected. An abrasive surfaceupon at least one of the retention members increases the grip betweenthe retention member and the screen thereby reducing the likelihood ofthe screen slipping when held by the retention member.

The apparatus may comprise a pigmented reflective member in an opticalpathway between the projector and the screen. The pigmented member mayreflect only part of the visible spectrum of light, typically thepigmented member will appear grey or white to a viewer.

It has been found that the use of a grey reflective member in theoptical pathway between the projector and the screen reduces the outlineof the reflective member upon the screen compared to when a whitereflective member is used, and also reduces the level of the milky whitehue associated with the projector emitting light where there is no imageof an object to be projected.

The pigmented reflective member may be inclined at an angle with respectto the plane of emission of light from the projector. The angle ofinclination of the member with respect to the plane of emission of lightfrom the projector may be variable. The member may comprise a pluralityof sections each of which may have an independently variable angle ofinclination with respect to the plane of emission of light from theprojector.

The inclination of the reflective member can compensate, at leastpartially and in some instances completely, for keystone effect. Thevariation of the angle of inclination or distance of the reflectivemember allows for a variation of the apparent depth and/or position ofan object when projected upon the screen. This is because the virtualimage appears as far behind the screen as the real image is in front ofthe screen.

There may be a reflective device, typically a mirror, arranged to directlight projected from the projector on to the reflective member.Typically, the reflective device is mounted upon an upper part of theframework. The reflective member may be parallel, or substantiallyparallel, to the reflective device. In some embodiments the projectormay be mounted upon an upper truss of the framework and may be alignedwith the horizontal, typically light projected from the projector isdirected on to the reflective device.

Such an arrangement compliments the keystone correction achievable bythe inclination of the screen and the reflective member and isparticularly useful where an HD projector is used in order to compensatefor the keystone effect without the use of the projector's processingpower.

The reflective member may comprise a mask corresponding to the apparentlocation of a prop in the screen to an audience. Typically, the maskwill absorb light over at least a fraction of the visible spectrum andpreferably the mask will be black. The mask may be arranged to producean area upon the screen upon which the image is not projected. The maskmay vary in extent and shape, for example by the use of a slidingelement that is moved in and out of position upon the reflective member.

The mask can be used to make the illusion of an article disappearing andreappearing behind a prop that is placed upon a stage, either behind orin front of the screen.

The apparatus may comprise a light source arranged to selectivelyilluminate an area of stage comprising the prop. The light source may bea white light source

Lighting the prop causes the prop to become more visible and betterdefined against the dark, typically black, background. This enhances thethree dimensional effect of the projected image interacting with theprop. Also directing bright light upon the prop serves to reduce thecontrast ratio of the projected image upon the prop, which typicallyremains slightly visible even when a mask is used in the prop's shadowupon the reflective member, thus enhancing the illusion of the projectedimage disappearing behind the prop.

The apparatus may comprise a light source arranged to illuminate atleast part of a stage. The light source may be located to the rear ofthe screen, typically along a top edge of the frame and/or along eitherside of the stage. The apparatus may comprise a plurality of lightsources. The apparatus may comprise a lighting desk equipped with fadersarranged to control the level of each light source, or selection meansarranged to selectively control the supply of power to each lightsource.

Such a light source is used in order that the colour and light levels ofthe area immediately surrounding the peppers ghost image, the stagebackground, can most closely match the colour of the projection surfacebackground, excluding the area on both which is carrying the image.This, reduces the milky hue perceived by the audience. The use of aplurality of light sources increases the uniformity of lighting of thestage, in order to produce a similar effect to the way light emittedfrom a projector hits the projection screen. By controlling each lightsource separately the lighting levels upon the stage can be controlledto closely match the levels of light as dictated by the showperformance, or the levels of unwanted light hitting the projectionsurface of the screen.

The projector may comprise a standard projector, for example a JVCML4000, or a Barco G5. Alternatively, the projector may comprise an LCD,or a television display. The display may comprise at least one elementarranged to be non-emitting in response to control from a processor. Theat least one element may form a mask arranged to produce an area uponthe screen upon which the image is not projected. The mask maycorrespond to the shape and location of a prop upon stage. The prop maybe three dimensional.

According to a second aspect of the present invention there is provideda method of providing a projection apparatus comprising the steps of:

(i) resting a frame upon a number of elevation means;

(ii) attaching leg sections to the frame;

(iii) increasing the height of the elevation means;

(iv) adding further leg sections;

(v) attaching a lower edge of a screen to a lower rear piece of theframe;

(vi) raising an upper edge of the screen to adjacent an upper frontsection of the frame; and

(vii) attaching the upper edge of the screen to the upper front sectionof the frame.

The method may comprise providing the elevation means in the form of ajack.

The method may comprise providing the screen in the form of a film. Themethod may comprise removing a roll of screen film from a protectivecylindrical casing. The method may comprise laying the screen upon adust-free protective sheet.

The method may comprise placing the lower edge of the screen betweenjaws of a first retention member and may further comprise securing thescreen in position using a fixing means passing through the retentionmember and the screen and a locking means arranged to lock the fixingmeans being arranged to secure the locking means in position. The methodmay comprise providing the fixing means in the form of a bolt and thelocking means in the form of a nut.

The method may comprise attaching tensioning means to the retentionmember adjacent at least some of the fixing means.

The method may comprise attaching the tensioning means to the lower rearpiece of the frame. The method may comprise attaching a second retentionmember to an upper edge of the film screen, typically in the same manneras the first retention member is attached to the lower edge. The methodmay comprise attaching tensioning means to the second retention member.The method may comprise providing the tensioning members in the form ofratchet straps.

The method may comprise attaching a rope to the second retention memberand passing the rope over the upper frame and using the rope in step(vii) to raise the screen.

The method may include tensioning each of the tensioning means such thatthe screen is flat and substantially wrinkle free.

The method may include depending a projector from the upper frame.

The method may include placing a pigmented reflective board between thescreen and a front edge of the frame. The method may comprise reflectinglight emitted by the projector from the board onto the screen.

The method may comprise forming the frame from a truss work.

According to a third aspect of the present invention there is provided aprojection apparatus constructed according to the second aspect of thepresent invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The invention will now be described, by way of example only, withreference to the accompanying drawings, in which:

FIG. 1 is a schematic representation of a first embodiment of aprojection apparatus according to at least an aspect of the presentinvention;

FIG. 2 is a side view of a the projection apparatus of FIG. 1 showing apigmented reflective member in first and second positions;

FIG. 2 a is a schematic representation of an alternative projectionarrangement, suitable for use with the apparatus of FIGS. 1 and 2;

FIG. 3 is a schematic representation of a second embodiment of aprojection apparatus according to at least an aspect of the presentinvention;

FIG. 4 is a perspective view of a screen clamping arrangement of FIGS.1, 2 and 3; and

FIG. 5 is a schematic view of a projection apparatus being constructedaccording to the second aspect of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIGS. 1, 2 and 4, a projection apparatus 100 comprisesa box frame 102 formed of trusses 104, a projector 106, a support frame108, a screen 110 held within the support frame 108 and a grey pigmentedreflective board 112.

The projector 106 depends from a front upper cross-piece truss 104 a ofthe box frame 102. The board 112 lies below the projector 106 at thebase of the box frame 102. The screen 110, is inclined at approximately45° to the horizontal and the front edge of the screen 110 is proximatethe front upper cross-piece truss 104 a of the box frame 102 and therear edge of the screen is proximate a stage 109 that lies to the rearof the box frame 102.

The screen 110 is typically a polymeric foil, which can have a partiallyreflective coating upon a front face of the foil. The screen 110 isretained within the box frame 102 by means of tensioning straps 114attached to the box frame 102, at the top and bottom edges of the screen110. At a free end of each of the tensioning straps 114 there is pair ofclamp jaws 116 which have respective openings 118,120 passingtherethrough. The faces of the jaws 116 are optionally coated with anabrasive 121, such as sandpaper, in order to enhance the grip of thejaws 116 upon the screen 110.

Edges of the screen 110 are placed between the jaws 116 and a bolt 122is placed through the openings 118, 120 and passes through the screen110. A nut 124 is threaded onto the bolt 122 and tightened to hold thescreen 110 between the jaws 116. The tensioning straps 114 pass throughthe trusses 104 and are tightened using a friction locking bucklearrangement 128.

Each of the tensioning straps 114 can be tightened or loosenedindividually so as to allow an even tension to be applied over the wholesurface of the screen 110 thereby reducing, and ideally eliminating, theformation of wrinkles upon the screen 110 which reduce the quality of animage projected upon the screen 110.

The reflective board 112 lies below the projector 106 adjacent to alower front cross-piece truss 104 b of the box frame 102. The projector106 is directed such that light emitted by the projector 106 strikes thereflective board 112. The board 112 is inclined so that the lightemitted by the projector 106 is reflected upwards from the board 112onto the screen 110. The use of a grey, or otherwise coloured board 112reduces the milky hue associated with light from the projector wherethere is no image to be projected.

A fraction of the projected light striking the screen 110 is reflectedfrom the front surface of the screen 110 where is can be viewed by anaudience. A presenter upon the stage 109 behind the screen 110 can alsobe viewed by the audience but does not interfere with the viewing of theimage by the audience.

The board 112 is connected to a hinge arrangement 130 along a rear edgethereof. The hinge arrangement 130 allows the board 112 to be raised andlowered, typically be a hydraulic ramp 132 controlled by a computer 134,in order to compensate for the ‘keystone’ effect. Alternatively, theboard 112 can be raised and lowered by the person pulling upon a string,or an electric motor to drive the board up and down.

The raising and lowering of the board 112 also allows for the audience'sperception of the positional depth upon the stage of an element of aprojected image to be altered by varying the height of the element ofthe image upon the screen 110. It is envisaged that the board 112 maycomprise a number of individual sections each of which may be raised anlowered individually in order to allow the perceived depth of anindividual element of an image to be varied independently of otherelements of the image.

A non-reflective mask 136 in the shape of a prop 138, in this example arock, is placed upon the board 112. The prop 138 is place upon the stage109, typically behind the screen 110. The mask 136 is placed such thatthe board 112 is obscured in a region corresponding to where the prop138 is located with respect to the screen 110. This arrangement of mask136 and prop 138 results in an image, or part of the image, projectedupon the screen 110 apparently disappearing as the image, or part of theimage, passes over prop 138 and reappearing once the image, or part, ofthe image has passed over the prop 138 as the mask 136 prevents lightbeing reflected onto the region of the screen 110 corresponding to thelocation of the prop 138. The mask 136 can be variable in size andshape, for example by means of a sliding panel that is moved intolocation and varied in size according to the size of the prop 138. Thisalso allows for the depth perception of props to be varied as theirapparent effect upon variable depth image elements, as discussedhereinbefore, can be varied appropriately, for example a given size ofrock will obscure proportionately more of a distant image than the samerock will of a near image.

A light source 140 is mounted upon the box frame 102 and illuminates theprop 138 in order to reduce the effect of any residual light reflectedfrom the board 112 onto the prop.

Referring now to FIG. 2 a, an alternative projection arrangement 200,suitable for use with the apparatus of FIGS. 1 and 2 with an additionaltruss, comprises the projector 106 depending from a truss 202 forward ofthe screen 110, an inclined mirror 204 of variable inclination dependingfrom a second truss 206 forward of projector 110. The projector 106projects an image on to the mirror 204 such that the image is projectedon to the reflective board 112 and on to the screen 110. The mirror 204is typically arranged to be perpendicular to the board 112, and inembodiments where the board 112 has a variable angle of inclination themirror 204 will usually be arranged to track, synchronously, with anyvariation in the angle of inclination of the board 112.

It will be appreciated that the term mirror is used herein to describeany reflective surface that reflects substantially all, typically inexcess of 50% preferably in excess of 80%, light impinging upon it.

Referring now to FIG. 3, a projection apparatus 300 is substantiallysimilar to that of FIGS. 1 and 2 accordingly identical parts to those ofFIGS. 1 and 2 are accorded similar reference numerals in the threehundred series.

A projection screen 306 resides in front of the screen 310 adjacent thelower front cross-piece truss 304 b. The projection screen 306 istypically a liquid crystal display (LCD) screen or a television screen.The projection screen 306 projects an image upwards onto the frontsurface of the screen 310. The use of a projection screen 306 removesthe ‘keystone’ effect associated with conventional projectors.

A mask 336 can be formed upon the screen by use of a computer 340 tocontrol the projection screen 306 to black out the appropriate part ofthe projection screen 306 electronically. This removes the need for aphysical mask to be produced. The computer 340 can be used to switch ofareas of the projection screen 306 which do not contain part of an imageto be projected, this reduces the milky white hue associated with suchareas when using conventional projectors. Also, the use of a computer340 to control the projection screen 306, together with image sizing inrelation to image movement allows an image to be readily scaled andpositioned upon the projection screen 306 to enhance an audience'sperception of depth and movement of a projected image using known imageprocessing techniques. Alternatively, the projection screen 306, orsections of the projection screen 306, can be raised and lowered underthe control of the computer 340 in order to enhance the audience'sperception of depth of the projected image.

Referring now to FIG. 5, a box truss framework 500 comprises a squareupper truss work 502 and leg trusses 504. In constructing the framework500 the upper truss work 502 rests upon a number of jacks 506. Firstsections 508 of the leg trusses 504 that extend at right angles to theupper truss work 502 are added at the corners of the upper truss work502. The height of the jacks 506 is increased to allow additionalsections 510 of the leg trusses 504 to be added until the desired heightof the box truss framework 500 is achieved.

A cross-piece truss 512 is fixed to two of the leg trusses 504 such thatit horizontally spans the gap therebetween at a height close to, andtypically slightly below, the level of a stage floor 514. The legtrusses 504 spanned by the cross-piece truss 512 constitute the rearlegs of the framework 500 and are located adjacent the front of thestage floor 514.

A dust-free protective plastic sheet 515 is laid across the width of thestage floor 514 in front of the rear legs of the framework 500. A rollof screen film 518 is removed from a protective cylindrical casing 520and is unwound across the width of the stage floor 514. The film 518 isplaced upon the sheet 515 in order to prevent damage to the surface fromdust particles or other sharp protrusions.

A lower edge 522 of the film 518 is placed between jaws 524 a,b of aretention member 526, each jaw 524 a,b having opposed openingstherethrough spaced at approximately 0.5 m intervals. Bolts 528 areplaced through the openings, and through the film 518, and secured inposition using respective nuts. Ratchet straps 532 are attached to theretention member 526 adjacent alternate bolts 528, having a spacing ofapproximately Im, and are then attached to the cross-piece truss 512.

A second retention member 534 is attached to an upper edge 536 of thefilm 518 in a similar manner to how the retention member 526 is attachedto the lower edge 522. Ratchet straps 538 are attached to the secondretention member 534.

A rope 540 is tied to the second retention member 534 and is passed overthe upper truss work 502 opposite the cross-piece truss 512. The filmraised into position using the rope 540 and the ratchet straps 538 areattached to the upper truss work 502. Both sets of ratchet straps 532,538 are tightened individually until the screen film is tensioned suchthat the film 518 is flat and, ideally, free from wrinkles.

A projector 542 is depended from the upper truss work 502 and apigmented reflective board 544 is placed between the screen 518 and thefront edge of the box truss framework 500 such that light emitted by theprojector 542 is reflected from the board 544 onto the screen 518. Thescreen 518 reflects at least part of the light from a front surfacethereof away from the stage and into an auditorium to be viewed by andaudience.

In order to prevent the audience observing the projection apparatus bothside and front drapes 546 are used to screen the apparatus from theaudience.

1. An image projection apparatus, comprising: an image source, a frame,a light source and an at least partially transparent screen; the framebeing arranged to retain the screen under tension, such that the tensionof the screen can be independently varied at a plurality of positionsalong at least one edge of said screen; the light source arranged toilluminate at least part of the apparatus; the screen inclined at anangle with respect to a plane of emission of light from the image sourceand the screen having a front surface arranged such that light emittedfrom the image source is reflected therefrom; and the image source beingarranged to project an image such that light forming the image impingesupon the screen such that a virtual image is created from lightreflected from the screen, the virtual image appearing to be locatedbehind the screen; wherein the screen is foil and the frame comprisesfirst and second retention members arranged to sandwich an edge regionof the screen therebetween; and wherein the first and second retentionmembers are connected to one or more flexible tensioning members, whichextend from the frame, the foil, flexible tensioning members and theframe lying in a common inclined plane, with the tension on the foilbeing applied in the plane of the flexible tensioning members and thefoil.
 2. The apparatus according to claim 1 wherein the foil ispolymeric foil.
 3. The apparatus according to claim 1 wherein: the firstand second retention members comprise respective openings therethrougharranged to collocate with respective openings in the screen; and theopenings are arranged to receive fixing members to clamp the screenbetween the first and second retention members.
 4. The apparatusaccording to claim 1 wherein the frame is arranged to retain the screenunder tension such that the tension of the screen can be varied at aplurality of positions along at least one edge of the screen such thatthe screen is substantially wrinkle free.
 5. The apparatus according toclaim 1 wherein the image source is a projector, an LCD or a televisiondisplay.
 6. The apparatus according to claim 1 further comprising apigmented reflective member in an optical pathway between the imagesource and the screen.
 7. The apparatus according to claim 6 wherein thepigmented reflected member is grey in color.
 8. An image projectionapparatus, comprising: an image source, a frame and an at leastpartially transparent screen; the frame being arranged to retain thescreen under tension, such that the tension of the screen can beindependently varied at a plurality of positions along at least one edgeof said screen; the screen inclined at an angle with respect to a planeof emission of light from the image source and the screen having a frontsurface arranged such that light emitted from the image source isreflected therefrom; and the image source being arranged to project animage such that light forming the image impinges upon the screen suchthat a virtual image is created from light reflected from the screen,the virtual image appearing to be located behind the screen; wherein thescreen is foil and the frame comprises first and second retentionmembers arranged to sandwich an edge region of the screen therebetween;and wherein the first and second retention members are connected to oneor more flexible tensioning members, which extend from the frame, thefoil, flexible tensioning members and the frame lying in a commoninclined plane, with the tension on the foil being applied in the planeof the flexible tensioning members and the foil.
 9. The apparatusaccording to claim 8 further comprising a light source arranged toilluminate at least part of the apparatus.
 10. The apparatus accordingto claim 8 wherein at least one of the faces of the first and secondretention members comprises an abrasive coating arranged to contact thescreen.
 11. The apparatus according to claim 10 wherein the abrasivecoating is sandpaper.
 12. The apparatus according to claim 8 furthercomprising a light source arranged to illuminate at least part of astage lying behind the screen.
 13. The apparatus of claim 8 wherein bothof the faces of the first and second retention members comprise anabrasive coating.